Simple jQuery Plugin

(function($){
$.fn.extend({ 
swec_hello_world : function(user_options) {

    return this.each(function() {
        var defaults = {
            'bgcolor'      : '#cccccc',
            'width'        : '400px',
            'on_load'      : function() {
                //callback function
                return "";
            }
        };
        //accept options from user
        var options = $.extend(defaults, user_options);
        //Creating a reference to the object $("#hello_world")
        var obj = $(this);
        //call init to setup the object
        init();
        
        function init()
        {
            obj.html("Hello World");
            obj.css({
                "background-color" : options.bgcolor,
                "width" : options.width
            });
            //execute a user hook function
            options.on_load();
        }
    });
}
});
})(jQuery);

<script>
$(document).ready(function(){
    $("#hello_world").swec_hello_world({
        "bgcolor" : "#ff0000",
        "width"   : "400px",
        "on_load" : function() {
            //this is defined in the plugin, will be called after object is created...
            $("#hello_world").css("height", "200px");
        }
    });
});
</script>

<div id="hello_world"></div>